More than half of the Silicon Valley companies founded in the past decade were led by at least one immigrant, according to a new study on the contributions of foreign-born entrepreneurs.

Nationwide, about a quarter of technology and engineering companies created from 1995 through 2004 had at least one foreign-born founder, according to the report by Duke University's Master of Engineering Management program.

The study comes as a new Democrat-led Congress convenes and gears up for what is expected to be another heated debate over U.S. immigration policy, particularly on the role of highly skilled foreign workers.

"What is clear is that immigrants have become a significant driving force in the creation of new businesses and intellectual property in the U.S. -- and that their contributions have increased over the past decade," said the report, which was released Thursday.

The Duke University report expanded on a 1999 study by UC Berkeley Professor AnnaLee Saxenian, which found that foreign-born scientists and engineers, mainly from India and China, played a critical role in the growth of the California economy, particularly in Silicon Valley.

The Duke University report was based on a survey of more than 2,000 engineering and technology companies founded from 1995 through 2004.

The report says more than 25 percent of the foreign-born founders were from India, while others came from countries such as the United Kingdom, China, Taiwan and Germany.

The study defined an immigrant-founded firm as having at lease one founder who was born as a citizen of another country before moving to the United States.

"The phenomenon I observed in Silicon Valley in the 1990s has not only continued, it has become a national phenomenon: the rise of immigrant entrepreneurs in the technology sector," Saxenian, who is the dean of the UC Berkeley School of Information, said in an interview.

"We often talk about immigration in terms of low-skilled undocumented workers," she added. "The high-skilled workforce is contributing directly to the U.S. economy by creating new firms, new jobs, new wealth. It's easy to assume that immigrants are always displacing U.S. workers. In this case, they are creating new opportunities."

He cited his organization's study from several years ago that said immigrants had higher rates of entrepreneurship than native-born Americans about 30 years ago. But that has changed over the past decades because most recent immigrants are unskilled, he said.

"The long and short of it is our current immigration policy doesn't by design bring entrepreneurs," Keeley said. "Instead, it brings busboys and nannies and landscapers because immigration overwhelmingly is from the undereducated, lower-skilled Third World."

Marcus Courtney, president of the Washington Alliance of Technology Workers, a union of high-tech workers, said the report ignores the negative impact of immigration, especially federal guest worker programs, on the country's technology workforce.

WashTech has been critical of federal guest-worker programs, such as the H-1B visa program, that allow U.S. tech companies to hire technologists and engineers from other countries.

Courtney said the report ignores the U.S. high-tech jobs that have been lost over the past several years because of offshoring and layoffs.

"The idea that the high-tech economy is only creating jobs totally ignores the fact that there was a deep recession," he said.